Hydrogen-rich syngas production via biomass pyrolysis catalyzed by iron co-loaded with biochar and aluminum smelting fly ash: Tar formation and component characteristics

Biomass pyrolysis for hydrogen production is generally regarded as a crucial technological pathway to achieve the carbon neutrality goals, whereas the corresponding system efficiency and environmental friendliness are significantly constrained by the generation of tar byproducts. In this study, the iron-based carbon-aluminum (Fe/Carbon-AWA) composite catalyst was prepared via the hydrothermal carbonization method using corn straw (CS) as the carbon-based precursor, and activated aluminum smelting ash (AWA) as the support. Besides. its catalytic effect on hydrogen production performance was systematically investigated, and the intrinsic relationship between tar conversion and hydrogen yield was further elaborated. The results demonstrate that when the Fe loading reaches 10%, the catalyst exhibits optimal catalytic activity with a hydrogen yield of 64.36 mL/g -biomass , a hydrogen selectivity of 39.96%. Meanwhile, the total gas yield of 161.06 mL/g -biomass can be achieved, accounting for 43.77% of the total product yield, whereas the liquid yield decreases to 36.44%. The full-component analysis of tar indicates that the light tar fractions are primarily composed of oxygenated compounds. In contrast, the heavy tar fractions are dominated by polycyclic aromatic hydrocarbons (PAHs) with a pyrolysis weight loss rate of only 54.24%. This limited pyrolytic reactivity represents the critical bottleneck in the tar conversion. It reveals that the Fe/Carbon-AWA catalyst can remarkably promote the cracking and conversion of refractory heavy tar components, and thereby the chemical energy stored in tar is partially converted into the hydrogen-rich syngas, resulting in an energy recovery efficiency of 17.72% and a carbon efficiency of 8.02%. Accordingly, this comprehensive strategy with the combination of waste-to-waste catalyst design and full-component analysis of tar was established. This work provides a feasible pathway for the synergistic development of biomass-based hydrogen production and waste valorization, which contributes to the efficient process integration and systematic optimization of biomass energy systems.